This is interesting! You did well creating an intriguing situation and used some pleasing imagery. A couple small things would make it even better, in my own opinion.
I would choose one or the other from the words crass and vulgar. Using both is a little redundant and I think the moment would be more effective with just one! When someone flinches, it’s a quick, fluid thing, right? The two words split by a comma makes the reader hesitate, killing that quick motion of a flinch.
I also think you can get rid of the comma after “have in common.” The comma breaks up the thought but there doesn’t seem like there should be a break in thought in the sentence.
Nice piece!

Thanks for the great feedback – I’ve made some edits! :)

She’s a piece of work. It kind of reminds me of ‘Play Misty For Me’, an old Clint Eastwood movie. She has all the makings of a very, very scary mistress.

She’s clearly completely crazy – and yet has some sort of magnetic hold over him. Compelling stuff.

Also, excellent use of an Old English expletive there; Chaucer would be proud.